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O r g a n i c C h e m i s t r y

O r g a n i c C h e m i s t r y. Martha Andreski. History.

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O r g a n i c C h e m i s t r y

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  1. O r g a n i c C h e m i s t r y Martha Andreski

  2. History • For many years, it was believed that substances produced by plants and animals could not be prepared in the lab due to the “vital force doctrine” (some mysterious life force was present in substances produced in living things) • In 1828, Friedrich Wohler synthesized urea ( CO(NO2)2 ), an animal waste product, from ammonium cyanate

  3. Organic Chemistry • Is a branch of chemistry dealing with the study of all Carbon compounds, both natural and artificial (with the exception of very simple compounds like CO, CO2) • Now, millions of organic compounds are known, with thousands being discovered or synthesized each year (Compare this to the about 25,000 inorganic compounds) • Well over 90% of compounds are organic

  4. Why So Many Organic Molecules? • A) C has a tremendous combining capacity since it has lots of possibilities in its valence level (it has 4 electrons and can gain or lose or share 4 electrons while bonding) • B) C atoms form covalent links with H, S, N, O and others, resulting in large numbers of compounds • C) the same atoms, when re-arranged around carbons, increase the variety

  5. Other Facts: • C links covalently, so e- are shared • C compounds have many isomers (substances with the same molecular formula but different structural formulas) • ie: normal butane and iso-butane • (n-butane) As the number of C atoms increases, the number of possible isomers increases. ie: C8H18 had 18 isomers; C10H22 has 75 isomers!

  6. Properties of Organic compounds • Not good conductors of heat • Not good conductors of electricity • Slower to react • More affected by T and P changes

  7. Types of Formulas

  8. Divisions of Organic Compounds • A) Open Chain, or aliphatic (acyclic) • ie: • B) Cyclic • ie:

  9. Aliphatic Compounds • There are 2 main types: • A) hydrocarbons – consist only of H and C • B) hetero-acyclic – something else is added to the H and C

  10. Order of Study • First, we’ll study the simplest hydrocarbons • Then we’ll add things to hydrocarbons • Then we’ll make them cyclic • Finally, we’ll make them hetero-acyclic

  11. Alkanes • “-ane” ending indicates that there are only single bonds b/w C’s • “formula” – CnH2n+2 (where n=the number of C atoms) • are therefore “saturated” (single bonds only) whereas if double or triple bonds are present, those molecules are said to be unsaturated

  12. Examples of Alkanes But it’s too tedious to draw complete structural formulas, so draw skeletal formulas instead ie: C-C-C

  13. Naming Alkanes • Alkanes are named based on the number of carbons in the longest continuous chain. • Memorize these! Go to Practice Sheet Do Number 1

  14. 1. Naming Alkanes requires looking for the longest continuous chain of carbons • ie: TRY THIS… …is called nonane since there are 9 carbons and there are single bonds between carbon atoms This is Octane

  15. Branching Alkanes • Often, alkanes have branches, such as  • Both of these are alkanes; in fact, both are octanes. Are they alike? • NO! • We must distinguish between the two using a set of rules that are designed to help you name even the most complex molecules.

  16. Naming Branched Alkanes • First, number the longest, continuous carbon chain from the side closest to the branch This is called 3-methyloctane 8 C’s Tells where the branch is Has only single bonds b/w C’s The attached group has only 1 carbon (and the “-yl” tells us it’s a branch Always used to separate numbers and letters Go to Practice Sheet A, Numbers 2 and 3

  17. 2. Naming Alkanes with branches requires the numbering of the molecule from the side closest to the branch • ie: TRY THIS… …is called 2-methylpentane This is 4-ethylheptane

  18. 3. Don’t be fooled by branch look-alikes! • ie: TRY THIS… …is called 3-methylhexane This is 3-methyldecane

  19. 5. A molecule might contain methyl, ethyl, propyl, butyl, pentyl, etc. groups • ie: TRY THIS… …is called 5-propyldecane This is 5-ethylnonane

  20. 6. A molecule might contain more than one branch; use prefixes to indicate how many groups are present • ie: TRY THIS… …3,5-dimethylheptane This is 4,5-diethyloctane

  21. 7. A molecule may contain more than one type of group; alphabetize the group types in the name • ie: TRY THIS… …3-ethyl-2-methylheptane This is 4-methyl-5-propyloctane

  22. 8. Number the C’s in a chain so that you have the lowest combination of numbers • ie: TRY THIS… This is 3,4-diethyl-6-methyloctane …3-ethyl-2,7-dimethyloctane

  23. Alkenes • “-ene” means “double bond” • General formula is CnH2n • C=C is called ethene • C-C=C is called propene • As the molecule becomes larger than propene, we must indicate the location of the double bond

  24. Larger Alkenes • As the molecule becomes larger than propene, we must indicate the location of the double bond • this is called 2-butene

  25. Alkenes that branch • If an alkene has a branch, the location of the double bond determines the numbering of the C’s. Choose the lowest possible numbers • is called 4-methyl-1-pentene • Notice: we name the carbon AFTER WHICH the double bond is found! Go to Practice Sheet; Do Numbers 9,10,11

  26. 9. It is not necessary to indicate the location of a double bond when there is only one possible location • ie: TRY THIS… …is just ethene …is propene

  27. 10. Indicate the exact location of a double bond by using the C number “before” the bond • ie: TRY THIS… …is 2-heptene …is 3-octene

  28. 11. A double bond is of more importance to C numbering than is a branch • ie: TRY THIS… …is 4-methyl-3-heptene …is 5-methyl-3-heptene

  29. Geometric Isomerism • Example: C4H8 • Has 4 isomeric alkenes (2 isomers of 2-butene differ in the spatial arrangements of the substituents on the double bond) cis-2-butene (both CH3 groups are “on the same side” of the double bond) trans-2-butene (CH3 groups are on “opposite sides” of the double bond)

  30. Occurence of Geometric Isomers • In alkenes whenever the two carbon atoms connected by the double bond bear two different substituents • cis = “same” • trans = “opposite”

  31. Alkynes • “-yne” means “triple bond • General formula: CnH2n-2 • C2H2 is ethyne (aka: acetylene) • C3H4 is propyne

  32. Positional Isomers • 1-butyne 2-butyne • Triple bonds undergo the addition and cleavage reactions of the sort that double bonds undergo • When the triple bond is at the end of the molecule (in “terminal acetylenes”), the single H atom is relatively acidic, making weak acid compounds. (the other H atoms are strongly attached and could only be removed by strong bases) Go to the Practice Sheet; Do Problem 12

  33. 12. Triple bonds and double bonds follow the same basic numbering rules, except that the names end in -yne • ie: TRY THIS… …is 1-pentyne …is 5,6-dimethyl-2-heptyne

  34. Polyenes • Compounds with more than one double bond • “alkadienes” – consiting of only C and H, no rings, and 2 double bonds • Alkadienes have a general formula of CnH2n-2 (same as alkynes) • Indicate the location of the double bonds by numbering the carbon atoms • C=C-C=C is called 1,3-butadiene • Generally, alkenes are much more reactive than alkanes. Most changes occur at the double bond. Go to the Practice Sheet; Do Problems 13,14

  35. 13. Two double bonds require a “di” before the “ene” ending, and the lowest C numbering must be indicated • ie: TRY THIS… …is 1,4-pentadiene This is 2,3-hexadiene

  36. 14. Yes, these can have groups, too! • ie: TRY THIS… This is 3,4,5-trimethyl-1,2-heptadiene …is 4-ethyl-1,2-hexadiene

  37. Hydrocarbons with both Double and Triple bonds (!) • Are named by replacing –ane by ‘-en-yne, -adien-yne, -ene-diyne, etc. • Example 1: • is 1,5-hexadien-3-yne • The smallest set of locants is used even if it results in –yne with a lower number than -ene

  38. Hydrocarbons with both Double and Triple bonds (!) • Example 2: • is 3-penten-1-yne (not: 2-penten-4-yne)

  39. Hydrocarbons with both Double and Triple bonds (!) • Example 3: • is 1,3-hexadien-5-yne • Regardless of the locants, the part of the name resulting form double bonds precedes the part resulting from triple bonds

  40. Cyclic Hydrocarbons • Formed by the removal of a hydrogen atom from each end and joining the two ends of the chain. (cycloalkanes) • General formula: CnH2n • Use the prefix “cyclo-” • Therefore, C3H6 could be cyclopropane or propylene • Cyclopropane is so common it has a “shortcut”:

  41. 15. In naming cyclic compounds, use the prefix “cyclo-” and the name of the alkane or alkene • ie: TRY THIS… …is cyclohexane This is cyclopentane

  42. Cyclic Hydrocarbons with groups • Suffix –yl designates a “functional group” formed by the loss of one H. Therefore, methane, CH4, is methyl as CH3. • Cycloalkanes tend to be unreactive • If double bonds are present – called cycloalkenes – but the presence of the double bond makes it more reactive • This is cyclopropene: methylcyclopropane 1,3-dimethylcyclopentane

  43. Cyclic compounds with one substituent group do not need numbers designating the location of the group • ie: TRY THIS… …is methylcyclohexane This is ethylcyclohexane

  44. Cyclic compounds with >1 substituent group MUST HAVE numbers designating the location of the group • ie: TRY THIS… …is 1,3-cyclopentadiene This is 3-ethylcycloheptene

  45. Since this structure is so common, it is given its own name “benzene” • ie: TRY THIS… …is 1,2-dimethylbenzene

  46. Since this structure is so common, it is given its own name “toluene” • ie: TRY THIS… …is 1,3,5-trinitrotoluene

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